1. Field of the Invention
The present invention relates generally to optical systems and, more particularly, to systems and methods for compensating for the effects of transients in an optical system.
2. Description of Related Art
In the field of fiber optic communications, systems transmit wavelength-division multiplexed (WDM) optical signals along optical fibers to increase the capacity of an optical communications link. A WDM signal includes multiple distinct wavelengths of light. Each of the wavelengths carries a respective optical information signal, known as an information “channel.” The number of wavelengths (i.e., information channels) in a WDM signal is a system parameter and usually ranges from 2 to 128 or more (in the case of “dense” WDM (DWDM)).
As the WDM signal travels through an optical network, it gradually fades and is, therefore, amplified at various points along its route. Because of the large number of wavelengths that can be carried by a single WDM signal, and also due to the high data rates of the individual information channels, amplification is typically performed by optical means.
Optical amplifiers can perform signal amplification using a doped length of optical fiber. Suitable candidate doping components for achieving optical amplification are rare earth doped-fiber amplifiers, such as erbium doped-fiber amplifiers (EDFAs). In an amplifier, it is possible to set the total output power level of the amplifier to a desired value, thereby establishing a relationship between the power of a WDM input signal entering the amplifier and the power of a WDM output signal exiting the amplifier. This also establishes a gain relationship for the information channels passing through the amplifier.
Ideally, the gain applied by the amplifier to the information channels remains at a constant value. Transients caused by the instantaneous addition or removal of one or more individual optical information channels affects the power of the WDM input signal. Although the amplifier instantaneously reacts to such a change in input power by providing a corresponding change in output power, thereby maintaining a constant gain for a brief amount of time, a natural recovery process is initiated soon thereafter by the amplifier, whereby the specified total output power eventually becomes redistributed among the new number of wavelengths (or information channels).
In the case of a channel being dropped, the effect of this transient will be an eventual increase in gain for the remaining information channels as the amplifier settles into steady-state operation. Conversely, in the case of an optical information channel being added, the specified total output power is shared (possibly unevenly) among the now larger number of wavelengths, leading to a decrease in gain for the information channels as the amplifier reaches a steady state.
The characteristics of these transients may depend upon the physics of the amplifiers, the number of amplifiers present, and possibly the distance between the amplifiers. Improper handling of the transients may result in degradation in the quality of the information channels reaching downstream components of the fiber optic network.
As a result, there exists a need for systems and methods for compensating for transients in an optical system.